Autism spectrum disorders (ASDs) are common, debilitating disorders affecting social interaction, communication, and repetitive behaviors. Recent genetic findings have identified mutations in synaptic cell adhesion genes and genes encoding their interacting protein partners at central synapses as genetic causes of autism spectrum disorders. This proposal will characterize novel and innovative autism mouse models that allow for brain development to take place with a genetic mutation. These particular models allow for reversal of the mutation at various times during brain development and ultimately in specific brain regions. The goal is to narrow the developmental critical period during which such mutations lead to altered brain function and atypical behavior. This information will allow scientists to focus specifically on the time periods and brain regions critical for generation of atypical behavior. In addition, these studies will substantiate feasibility of genetic and certain pharmacological approaches to treatment of a genetic form of autism. Progress to date is substantial in that the genetically reversible mutant mouse models related to autism have been established and characterization has begun.